Modern wind turbines are commonly used to supply electricity into the electrical grid. Wind turbines generally comprise a rotor with a rotor hub and a plurality of blades. The rotor is set into rotation under the influence of the wind on the blades. The rotation of the rotor shaft drives the generator rotor either directly (“directly driven”) or through the use of a gearbox.
An important auxiliary system generally provided on wind turbines is the pitch system.
Pitch systems are employed for adapting the position of a wind turbine blade to varying wind conditions. In this respect, it is known to rotate the position of a blade along its longitudinal axis with respect to the rotor hub aided by a slew bearing.
This slew bearing normally comprises an outer ring, an inner ring and, between these two rings, one or more rows of rolling elements which allow both rings to rotate relative to each other. In some cases this type of bearing may comprise a gear which meshes with a drive pinion.
These bearings normally include an annular chamber for retaining the rolling elements. The bearing chamber is normally built from two annular components known as raceways, more particularly outer and inner raceways having interior surfaces which form the radial walls of the bearing chamber. A lubrication fluid, such as oil or grease, is normally contained within the bearing chamber in order to reduce the friction between the components and also to assist in the dissipation of heat. A circulation system may further be provided to inject and/or drain lubrication fluid into the bearing chamber.
The loss of lubricating effectiveness may result in accelerated wear of the bearing elements.
Thus, proper lubrication of the bearings must be provided and maintained, in particular lubrication of the contact areas between raceways and rolling elements arranged inside the bearing chamber. Such lubrication may be particularly complicated and expensive due to the complicated accessibility of such contact areas.
Document U.S. Pat. No. 7,077,630 describes the lubrication of a pitch system of a windmill wherein the spacing between the rolling bodies of the bearing and the teeth of the gear is very small and the bearing arrangement and the teeth are disposed in the volume region of a lubricant chamber. The lubricant chamber has the form of a circular ring which is coaxial with the bearing and the gear and which has two radially outer wall regions separated from each other by a gap which permits the rotary movement of the two wall regions with the rotor blade and the hub respectively. Such an arrangement is rather complicated and adds the extra weight of the lubricant chamber to the system.
Document U.S. Pat. No. 7,470,111 describes a wind turbine wherein a blade bearing includes an inner ring that is firmly fixed to the rotor hub and an outer ring that is fitted with a toothing and is firmly connected to the rotor blade. A lubrication pinion is situated next to the drive pinion and underneath a cover means. Such cover means protects the lubrication pinion (and the drive pinion) against corrosion and contaminants. This is an expensive solution and the complete sealing of the cover may be difficult to achieve. If the sealing is not complete, the cover may not give an adequate protection against extreme temperatures and humidity.
Thus, there still exists a need to provide a cost-effective lubrication system for lubrication of the contact areas between raceways and internal rolling elements arranged inside the bearing chamber.